So before the sun went down and the temperature dropped to really-bleeding-cold, I swapped out of my work clothes and into sneakers and windpants and hit the sidewalk outside my hotel.

After my five minute warmup, I started my first stretch of running, 5 minutes of solid leg-pumping action. Ninety seconds in I was sucking wind and cursing the world.

Albuquerque, as some of you might be aware, is about 1,600 meters above sea level. If you're interested, here's a handy chart. That chart says that the pressure at this altitude is about 84.3 kPA, meaning that the partial pressure of Oxygen at this altitude is about 80% of what it normally is.